Recently electrochromic display devices have been studied as candidates for electronic paper type of displays. However, the slow switching speed and high power consumption of the electrochromic display technologies commercially available today do not meet the needs of the display market. Lately the trend has been towards the use of nano-materials, such as chemically modified nano-structured mesoporous films, for improving performance. Use of such materials has shown promising results. However, one of the remaining key issues with respect to electrochromic displays is the generation of color.
One prior art approach suggests selective color generation using a four layer light filter which comprises five transparent plates each having electrolytes formed on their facing surfaces. The plates, being glass or plastic, are coated with tin oxide or thin metallic transparent conductors on their facing surfaces. Disposed on one of the electrodes of each pair of facing electrodes is a thin layer (0.01 μm to 0.1 μm) of an electrochromic conducting polymer. Although four layers have been described, it is suggested that two or more layers may be used in any combination of voltages to allow the transmission of different colors and tints through the panel. A system of this type is disclosed in U.S. Pat. No. 4,749,260.